The present invention relates to the construction of styli used for writing or drawing purposes and in particular to the method of inserting the small ink tube in the point of a tubular stylus, the writing or drawing ink tube being inserted, centered and fastened with the assistance of an assembly tool within an aperture in the stylus.
Various methods are known providing for securing small ink tubes in the tips or points of the stylus. According to the known methods, the ink tubes are either glued or press fit into the bore of a finished plastic tip. Also it is known to place the tubes in a spraying or molding device and then cover them with plastic. In another method, the ink tubes have been glued or pressed into plastic tips which are themselves surrounded by metal casings.
All the mentioned methods have considerable drawbacks and difficulties in that they either take considerable time for glueing and permit only limited adhesive bonding and poor stability of the small ink tube when press fit into the plastic. Satisfactory adhesive action is obtained only under compression with both the bore in the point and the diameter of the pressfit portion of the small ink tube are perfectly matched in diameter to provide a uniform press fit for all tubes in a manufactured set.
For this reason, both the ink tubes and the tips must be made precisely to secure the necessary fastening connection. This involves an expensive operation. Another disadvantage arises from the pressing of ink tubes into bores of plastic tips. Under such conditions, they are exposed to a considerable degree of tension and stress. As a result, the adhesive bond, under changing climatic conditions breaks down. In this way the tube becomes loose from the tip and can no longer perform its function.
Where the ink tube is provided with an adhesive layer or coating sprayed or extruded thereonto, a complicated device must be used for securing the ink tube position during the spraying operation. This involves the danger that the writing area of the tube would suffer damage to become a waste product.
Both the process for glueing and pressing ink tubes into metal casings have the drawback that the casings and the press fit portion must be manufactured with a great deal of precision. Besides, where the fastening or fixation of the ink tubes is performed by glueing, a time consuming cleansing must follow the glueing operation, which by itself is sensitive and hard to control.
It is the object of the present invention to provide a method for forming writing instruments of the type described which overcome the disadvantages of the prior art.
It is another object of the present invention to provide a simple, economical process for forming writing instruments of the type described.
It is still another object of the present invention to provide a method for forming writing instruments of the type described which avoid the disadvantages of glueing, press fitting or plastic molding by providing for the bonding to be obtained by ultrasonic energy.
It is another object of the present invention to provide a method of mounting said tubes into said casings and tips in a simple and reliable operation connected with less cost and not requiring a precise manufacture of the tubes and/or tips.
Still another object of the present invention is to provide a method of ultrasonically welding the writing ink tubes to writing tips made of a plastic material and attached to casings of styli in order to fasten the tubes to the tips by means of a connection which is free of tension and stress and provides a secure and reliable hold unaffected by various climatic conditions, their changes and/or by pressure accompanying writing or drawing.
These objects and others, together with numerous advantages will be found in the following description.